Most of the online reviews on AirAsia seem positive, but some of them also say they are a stickler on weight if the flight is full. The max for carry-on is 7kg/15.4lbs, so it's likely you may have to check-in even if all you have is carry-on. But I haven't seen any online reviews complaining about theft out of luggage, or lost luggage. Checking in luggage is another $10 US and up depending on weight.